Brake operating mechanism



J. G. INGRES pw BRAKE OPERATING MECHANISM Filed June 22, 1942 gli@ Patented Decfl9,

UNITED STATES PATENT oEFfifcE BRAKE OPERATING MEQHAMSM Jeannot G. Ingres, Detroit, Mich., assigner to Auy tomatic Shifters, Inc., Richmond, Va., a corporation of Virginia Application June 22, 1942, Serial-No. 447,993

16 Claims. (CL Gil-54.5)

This invention relates to brake operating mechamsms.

One of the serious obstacles to the luse of power f booster brake operating mechanisms has been the use of mechanical controlling and operating means connected between the brakepedal vmechanism and the power mechanism. This has been due to the diillculty in. utilizing the extremely limited spaces available for the power mechanisms and the mechanical connections for oper-o ating them. Recently there have been developed brake operating mechanisms which overcome this diillculty. by eliminating the use of mechanical operating connections, the power mechanisms being operated and controlled hydraulically through the medium of pipes connected between the masf ter cylinders of the 'braking systems and the power mechanisms.- lSuch an expedienteliminates all mechanical connections leading from the brake pedal; thus permitting the powermechanism to be placed in any available space regardless of its location with relation to the brake pedal.

While hydraulically controlled lpower mechay nisms, of the type referred to are highly advantageous for the reasons stated,` they possess some disadvantage in operation Vin that the response' oi the power source to the hydraulic operation of the valve mechanism is slightly'sluggish, and thev same is true of the cutting 'o'ii of the power when movement of the brake pedal is arrested. The slight lagging of the responseof themotor to movement of the brake pedal has been partially overcomerby utilizing initial movement of the .brake pedal for displacing from the masterE cylinder into the braking system -suiiicient brake iiuicl to initiate movement of the brakeshoes' to take up play between the brake shoes andthe brake drums prior to the energizatlon of the power device.

An important object of the present invention is to provide a highly-eflicient brake operating mechanism wherein all sluggishnessl in the operation of the power device with respect to operation oi' the brake pedal of a system of this character is r completely eliminated, energization of the motor.

taking place from a practical standpoint instanfluid-operated valve without the use oi.'

A further object is to provide a control cham;

ber into which brake iluid is Ldisplaced from the master cylinder, and/ to provide two elements movable by the brake `fluid one connected for operation by the motor yand the other, of limited diameter, immediately movable upon the flow of fluid vinto the chamber '.when the brake pedal is depressed, whereby such smaller element moves a distance relative to the distance of movement of the piston or thev master cylinder which is inversely proportional to the area of such smaller element withrelation to the area of the master cylinder, thus providing for an extremely rapid initial movement of such smaller elementand I .consequently of the valve element controlled thereby.

A further object is to provide a Adevice of this character wherein the use of any means for manually displacing brake fluid into the iluid system leading to the brake cylinder is eliminated because o! the operating characteristics of the valve mechanism. v l

A further object is to provide such a mechanism wherein the brake pedal is provided with taneously with the operation of the brake pedal.'

Aiurtherobject is to provide a novel arrangement of parts in an apparatus of this character whereinfinitial displacement of brake huid from the master cylinder multiplies the' relative move. ment of the fluid operated valve of the .power device, vthus providing for extremely rapid energiaccurate feel" proportional to lthe force being exerted-in applying the brakes. l

Dther objects and advantages of the invention will become apparent during the course of the following description.

. In the drawing I-have shown two embodiments of the invention. vInthis showinsl Figure l is a central longitudinal sectional Aview l through thepower device, the brak pedal and its master cylinder, the brake cylinders for the wheels and the various piping connections being diagrammatically illustrated, f

Figure 2 is a transverse sectional view onlinel 2 2 ofFigure lgand,

Figure 3 is a fragmentary central longitudinal sectional view showing a modiiied form of the by a piston I2 operable by the brake pedal I3. 5

Fluid displaced from the cylinder -II ilowsr through a pipe I4 to operate a power rmechanism indicated 'as -a whole by the numeral I5 and referred to in detail below.` Fluid is displaced from' .thepower mechanism througha. suitable pipe' l0 line diagrammatically represented in Figure 1 and indicated by the numeral I6, this pipe line having suitable branches'leading to the cylinders I'I of the rear vehicle wheels and the cylinders I8 of the front vehicle wheels. t. l5

The power device I5 comprises a cylinder I9 having heads 2li and 2l each of which is provided with a preferably integral axial extension aseshown, in Figure 1. The extension on the head v2i) is indicated bythe numeral 22 and its 20 interior space 23 constitutes a vpressure chamber communicating with the pipe line Isd that brakeiluid displaced from the chamber 23 ilows Y under pressure to the' brake cylinders I1 and 18. .The axial extension on the head 2| is in- 25- .dicated by the numeral 24 and the space with- -inthisextension at its outer end, vindicated by; the numeral 25, is the control chamber for Ythe device and communicates with the conduit -Ie to receive brake fluid displaced from the master 304 cylinder.

' A piston unit 25 ismounted for reeiprocation in the power device. This unit comprises a disk 21 at the periphery of which is mounted a cup 25 which may beiurged outwardly by an expansible ring 29 85 held in positi n bya retainer 3|), rivets or the like l`I passing .hrough the retainer, through a lamping ring 32 and through the cup 28 and disk 21 to secure these 'elementswith respect The piston unit is provided with a sleeve indicatedas a whole by the numeral 34, this sleeve having two ends 85 and 36 projectingaxiallyto for reciprocation inthe cylindrical chamber 23' and lis provided'with suitable packing 3I.` The end of the'sleeve remote from the disk 2'!4 is reciprocable in the extension 24 and is also .5

provided with suitable packing sa. It win be apparent that the body of the sleeve section 35 is of substantially smaller diametervthan the interior of the extension 24, thus providing a space' 29,' 'andthisspace` is open to the atmosphere 5' preferablythrougha suitableair clem; 40.

The internal diameter of the extension24 bears Ae. deilnite relationship to lthe diameter' ofA the cylinder II. In actual practice these; diameters are equal, the cylinder II inV Figurer 1 merely 400 being'shown diagrammaticallyvwithout `referenc to any particular sizel relati e"to the normal diameter of the extension 24. Y These relative diameters' are'important 'in the practical operation of the mechanism.- as bereferred to' n later.' The internal diameter of theextension z2 isl preferablyy equal te the internal diameter l of the 'extension 24 rso that ythe amount of fluid displaced from the pressure chamber 2,3 in the operation of the mechanism will be equal to the 70 amount of iluid displaced from the mastercylinder intothe operating chamber 25, as wil1`be Vcome apparent.

f A valve plunger 4I isxmounted for reciprocation in a cylindrical bore 42 formed throughout 75,/ p11'` e1 of oil in the chamber 2s will' be dupliend of the recess di.

, the length of the sleeve section 35 and through a portion of the sleeve section 35. Beyond the bore 42 the sleeve section 35 is provided with a smaller bore 43 in which the adjacent end of the valve plunger 4I is reciprocable. The Ylatter `end of the valve plunger is provided withsuitable packing 44, while the oppositefend of the valve plunger reciprocable in the bore 42, is suitably packed as at 45. The latter packing is arranged against a land 46 formed on `the valve plunger and spaced a substant al distance from another valve land 41 forme on the valve plunger. The space 48 between these two lands communicates with the air space 39 through A ports 49.

In order to prevent direct. communication between theair space 39 and the adjacent end of the cylinder I9, suitable packing tu is carried by the head 2l in sliding engagement with the sleeve section 36, Vand the latter element is provided with an annular ange 5I engaging the head 2i -to' limit movement of the piston unit 2@ to the leftas viewed invFigure 1. Between the disk 2l and ange 5I 'the sleeve Se is provided with ports 52 having limitedA communication with the space 53 surrounding the valve plunger il to the right of the land 47 as viewed in Figure l. The land 41, in the "05 position of the parts, slightly uncovers the ports 52 for thev purpose stated, and the space. 53 communicates with the interior of the right hand end of the cylinder I@ through a port 54 formed in the sleeve section 35.

The right hand end of the cylinder i/is in constant communication with a source of partial vacuum s'uch as the intake manifold of the vehicle engine, a pipe 56 connected to the manifold being in iixed communication with: the cylinder through a port 51 formed in the head 2t. It

` will be apparent that .when the partsare in the teeach other.` A convolute spring 33 urges the 40 piston unit toward the left as viewed in Figure 1.

o iI" position, therefore,'the constant vacuum in the-right hand end of the cylinder I9 will be established in the left handend of this cylinder through port 54, space 5l and ports 52, thus. l A vacuum suspending the piston unit 2t.

the'right and left respectively of the disk 2'I. .45, f The end of the sleeve. section 35 is mounted A light spring 55 urges the valve plunger fili tc .its oif'positionhown in Figure 1 and its movement is limited in any suitable manner, for example, by a pin 59A extending through the left hand end; of the sleeve section 36. Movement .of the valve plunger in the opposite directionis limited by a flange 80 formed on the valve plunger andpengageable with the adjacent end of the v bore 42. Play between-the ange Sii and the end of the bore 42 will be taken up toi-the manual operation `of` the piston unit and the sleeves fconnected thereto'upon a' failure of power in l the power device.

engagement with a seat 6E formed at the'jinner The valve plunger is provided with an axial bore' 6,6 communicating with the control chamber. 25, andthe other end of the valve plunger is provided with a very restricted bore S1 extending through the' right hand limit of the valveplunge'r. The latter end of the valve plunger,l in the oil position of the parts, has a slightclearanceufor example l/qt" with respect tune vaus: asians engages this dass promptly upon,operation of the valve plunger.

'. Such movement will unseat the vdisk 84 and this ele t is'provid'ed with aportBS so that the asoman Y 3 i vide for the replenishing ofbrake fluid leaking, .5,

from the chamber 23, pipeline I9 and brake cylinders I1 and Il, in a manner to ibe described.`

In Figure 3 of the drawing a modified form of the invention is shown wherein the means for vreplenishing leakage from the pressure end of l0 the system is eliminated, the modified vform of the device being substantiallysimplifled. The cylinder head 29, axial extension 22 and pressure chamber 29 are identical, with the forms of the invention previously described and accordingly 15 have been indicated by the same reference numerals. r.

Referring toFigure 3, the numeral 69 designates a modified form of sleeve carried by the piston unit 28 in place of the sleeve 95 previously `20 described. The sleeve 69is`provided with a head 19 reciprocable in the pressure chamber 23 and sealed with respect thereto by a cup 1I which i.

preferably is formed of rubber, although it may be made of any suitable deformable material. 25

The annular flange of the cup 1I slides in the extension 22 sealed against the leakage of brake Y' fluid, and the cup completely covers the end of the head 10 and thus forms a seal for a bore 12.

A valve plunger 13' is substituted-for the valve 30 plunger 4I and has ltsright hand endas viewed in Figure 3 slidable in the bore 12.4 This bore connects with an enlarged bore 14, a shoulder 15 being formed between the two bores for engagement by an annular flange 19' carried by the 35 movement of the piston I2 is then arrested. to

plunger 19. This plunger 'obviously is movable vaxially relative tothe sleeve 89 and when its eittremity moves to the Vrighi; beyond the head 1I, the central portion of 'the cup 1I will be d e.

f the left in Figure l to displace nuid from the cylinder II through pipe line I4 into the operating chamber 25.' As previously stated, the internal diameters of the extensions 22 and 24 and of the cylinder II are preferably equal, for a reason which will become apparent, and the cross-sec- Y tional area of the bore 42 is preferably one-third the intemal cross-sectional area of the extension 24, and accordingly one-third of the cross-sectional area of the cylinder I I. If this proportion is followed in the cross-sectional/area of the parts referred to any linear movement of the piston I2 wiu be multiplied by three in the linear movement of the valve plunger 4I. Thus a. 1/8" movement of the piston I2 from its normal position would eifect a ya movement of the valve .plunger 4I to the right in Figure ll, it being noted that in the initial operation of the apparatus the piston unit 26 and the elements connected thereto are stationary.`

'I'he substantial movement of the valve plunger 4I relativeto movement of the piston I2 results in instantaneous movement of the valve land 41 from its olf position in Figure 1 to a position wherein the ports l2 are cut oi! from the vacuum -space 93 and are placed in full communication with the atmosphere through the space 49, ports 49,'space 29 and air cleaner 40. There will be an immediate extremely rapid increase in pressure .in the left end of the cylinder I9 (Figure 1 to cause an immediate response of .the piston unit ilu: movement of the piston I2 and valve plunger Assuming that the piston I2 has been moved %"-and the plunger 4I as stated above, and

maintain a slightapplication of the brakes,v the energization of the motor I! will effect movement of the plunger sleeve 35 so that its right hand formed and the pressure against the cup 1I will 40 `end will displace fluidifrom the pressure chamber react against the end of the plunger 13 to provide they brake pedal with "fee .as -will be described later.j The modified form of the invention is also preferably provided with the spring 58 tend- 'ing to move the valve plunger toward theleft to 45 its oil' position.

The` operation of the form of the invention shown in Figures 1 and 2 is as follows:

Theright hand end of the cylinder I9 (Figure 1) is in nxed communication with tnefinteke manifold SB through a suitable pipe line'it. The valve elements are shown in their Anormal or on lpositions in Figure 1,. and accordingly the partiel vacuum in the nent nana end of the er1f inderwiil be duplicated 'in the opposite end of 55 the cylinder through, port 54, space I3 .and` ports n, tneietterfbeing slightly uneevereaby the land v4-1. Thus it' will be apparent that the pis. ton unit 2l will be vacuum suspended. Under the conditions referred to the spring 459' will'hold' the V60 left hand end of the veiveplu ger uagemst th( stop pin Il and the spring 33 i-llhold the piston unit in its left hand limit of movement with the flange I I inl engagement with-the adjacent 'portionof the cylinder 'head 2L# The disk 84 will 65 be engaged against itsfse'at tu with' the' adjacent end of thefvalveplunger 4I slightly clearing the' disk 64, for example, by approximately Uni'. and

when the brake isto be operated, the pedal is 23 into the brakingsystem through the piping I6.

Since the area.. of the valve plunger 4I is onethird of the interior cross-sectional area of the f .extension 24-it follows that the area of the end of the extension 96 will be two-thirds the interior cross-sectional aea of the extension 24 and twice ,the area of the left hand end of the valve plunger-f4I.

gization of the motor I5 in the manner stated, movement of the piston unit 26 toward the right will similarly move the left hand end of the ex-- tension 39 and since the plunger I2 is being maintained stationary, no brake fluid will be moving into the chamber 2s te satisfy the requirements of the space in the chamber 29 which will have necessarvfiuid to replace the space evacuated by the end of the plunger sleeve. After energize.- tion of' the motor Il, therefore, the valve plunger 4I will move back toward the left one-quarter inch so that its net movement is V3, andthe brake-mnd displaced bysuch V4" backrnove-y ment of .the plunger- 4I will provide for a V," movement of the 'sleeve I9.' this sleeve being double the-area of the h ad 4I, as stated.

From the foregoing it will be'apparent lthat any movement er the piston i: win remit 'in ex- '.actly the same net movement'of the valve plunger 4I and sleeve 3l, the valve ,plunger 'first overru'ne will be depressed to move the piston I2 i',ojward lfningjhe'distance of movement of the piston l2 Therefore it will be apparent that upon ener-v will equal. the iiuid displaced and then moving back two-thirds of the previt ously moved distance after the motor has been actuated. Since the internal diameters of the extensions 22 and 244 are equal, the operation referred to will result in movement of the'right harid end of the sleeve 35 todisplace from the pressure chamber 23 an amount of brake fluid equal to that which has been pumped into the control chamber 25. The amount of' uid forced into the brake cylinders i1 and I8 therefore,

II, the same as if the brakes h d been manually operated. However, the motor 'I5 will have performed most of the work in applying the brakes, thus requiring much less effort on'the part of the operator.

the right es viewed in Figure .1' te en extent pmportional to the area of thebore 43 with relation `to the cross-sectional area of the extension 22.

'.Therefore, the pedal I3 is always provided withfeel which is substantially exactly proportional Y to the pressure in the chamber 23. In, this con, nection it will be noted that theA spring 38 is very rom the cylinder The multiplication in the movement of the g valve plunger 4I with respect to movement of the piston I2 is important for two reasons. In

- the iirst place, it provides for an extremely rapid energization of the motor so that, so far as can be detected, the motor I5 operates simultaneously with the depression oi the pedal AI3. In the sec ond place, the relative areas of the ends of the plunger 4I and sleeve 36 provide for an extremely rapid. cutting off of the motor 'when'the'bra-kes have been applied to an extent corresponding to the extent to which the brake pedal has beendepressed. Reverse movement of the valve plunger 4I4 to the left upon energization of the 'motor takes place with the piston unit 26 moving toward the right,` andaccordingly there will be rapid relative movement between the ports 52 and land 67 to tend to restore the parts to their normal positions to cut off further energization y of the motor. Thus the motor is instantaneously responsive to pedal operation and the piston unit 25 stops instantaneously upon the stopping of the movement of the pedal I3. f l When the-,pedal I3 is stopped with the motor I5 energized the parts obviously will not return fully to their relative normal or "off positions. If the parts were returned to such positions, vacuum suspension of the piston unit' 28 would occur and the spring 33 would start to move the piston unit toward the left to slightly` release the brakes. What actually happens isthat in the relative movement of the parts to cut off the admisslonof air through ports E2 when pedal movement is stopped, the land 41 will move relatively toward the left until the admission oi' air is cut oil,

light, being of only sumclent tension to tend te hold the disk 64 on its seat.

It willl be apparent from the foregoing that ends ofthe motor so that the spring 33 will urge the piston unit toward the left, this operation being assisted by the brake fluid being returnedv to the pressure chamber 23 by the springs of the individual wheel cylinders I'I and I8. If the brake pedal I3 is partially released and its movement stopped, no. more il-uid will be displaced from `the chamber 25 into' the cylinder II, and slight additional -movementof the piston unit 2S 'toward the left will increase pressure in the chamberl 25"to quickly move the valve plunger 4I to the right,l thusinstantaneously cutting oil communication between the ports 52 and vacuum space 53 unit 25.

After'the brakes have been completely released the' parts will return to the relative positions shown in Figure 1. If.,there has been anylslight leakage of brake uid {iromgthe pressure end of I thesystem; there will be a'slightly smaller volwhereupon movement of the parts will bev 4 promptly'arrested. Y Any tendency for Vthe piston unit to move too far to the right in Figure 1 will result in very slight opening of the ports 52 to the vacuum space 53, thus immediately exhausting sumclent air from the left lend ofthe cylinder I9 to prevent further movement of the piston unit 25 toward the right. 'n

The slight clearance between lthe right hand end of the valve plunger 4I (Figure 1) and the disk B4 is taken up when the motor is energized.

the land Il always occupying a position sumciently to the right of its relative position with respect to the ports 52 when -themotor I5 is energized to slightly unseat the disk 5 4, Therefore, it will bel apparent that always', during' energizationoi' the motor I5, the disk 53 acts as a valve closing the end oi.' the passage 51, thus preventing leakage of brake iluid from the chamber 23 into the chamber .25.

During energization of the' motor, the port 58",

Figure 1, serves the function of exposing the acijacent end of the valve plunger 4I to a pressure in the chamber 23, andl this pressure therefore opposes movement of the valve plunger toward ume of iiuid in the pressure end of the system thanbefore operationpf the brakes. Undersuch conditions the movement of the piston unit and the valve plunger completely to their"off positions will create a slightly lowered pressure in the pressure end of the system, whereupon bralr ing uid *will flow through the bore 85 and passage 81 and-thence' through the"port 32 into the pressure end of the system until the pressures are balanced in the chambers 23 and 25, and this point will be reached when the amount of uid thus ilowing into the chamber 23 exactly equals the fluid which has leaked from the pres- `sure end' of the system.

It. will be noted that movement o! the valve plunger Ito the right (Figure 1) with relation to the piston unit as a whole is limited in accordance with the space between the flange or head 30 andthe adjacent extremity of the bore 42. Il.'

i rany reason,"'thepowe`r oi themotor should ail when the brake .pedal'is operated, the plunger 4| will move totherlght to itslimit of movement, whereupon the fluid pressure gen' erated in'the operating chamber 25 will'move' both the vsleeve 33 and plunger 4I- to displace iluid from the chamber 23.. /Attention is again invitednto the fact that the cross-sectional area of the cylinder `II and'the internal cross-sectional areas of the extensions 22 and 2| are equal to each other and accordingly the manual oper' ation ot th'e apparatus, in the event of power failure, will be exactly the same as if the pipe Il were directly connected to the pipe I6.

In4 the modified form of the invention shown to resist movement of the piston :,soaevi 5 plunger 4I, the same valveelements being pro-)10 vided and the plunger 13 being yurged towar the left in the same manner as the plunger 4I is urged to the left in Figure l.

The valve plunger 13 is operatedupon depression of the brake pedal in the same manner l5 that the plunger Il is operated audits movement to the right is permitted by the deformability of the cup 1l. This operation is provided solely for the purpose of utilizing pressure in the chamber 23 to react against the ad- 20 jacent end of the valve plunger -13 "to resist movement of the brake vpedal and thus provide the latter with feel.

' In previous mechanisms' of the same general type as theI present one, some sluggishness has 25 been experienced both in the energizing of the motor and in the arresting of the movement of the piston when movement of the'brake pedal is stopped.y In some of these prior structures slugof the brake pedal has been partially overcome by utilizing initial movement of the brakepedal in one way or another to manually displace uid into the pressure end of the braking system. to

take up play between the brake shoes and the brake drums so that| thismuch of the opera.- tion can be accomplished prior t6 energization of the motor, so that a lagging in the energization of theA motor is a less serious problem than lit otherwise would be. In some prior construc- 40 tions ,the result referred to is accomplished by initially by-passing some of the brake fluid from the inlet end of the mechanism to the outlet end thereof upon depression of thefbrake pedal,

but when this isV done,l the pressure' operation of 45 the valve does/not take Aplace until after play has been taken up between the brake shoes and 1 Ibrake drumsn Therefore, sucha system; While displacing fluid at the same rate inthe pressure end of the system aslt is displaced from the mas'- 50 ter cylinder, is oirlittle practical use since it merely conditions the brake shoes for operation andthe sluggishness of the motor is not overcome. In another type of prior mechanism,

the valve plunger itself enters the ressure champ 5 ment of parts may be resorted to without departtageous over the other type referred to in that it tends to initially take u'p play betweena the lbrake shoes and brake drums at the same time the valve mechanism is operated, lthus reducing the eiect of the sluggishness in the response of the motor. However, this is not suiilcient l to wholly overcome' sluggishness in motor reof iluid forced i'to the pressure end of the system is substantially less than the amount of iluid displaced from the master cylinder.)

With the arrangement employed in the present '(10 device it is unnecessary either to initially bypass brake iluid from the master cylinder into thelbraking system and Iit is'likewise unneces sary to displace brake duid by operation'of the valve itself. All tendency toward sluggishness in operation is removed by providing the arrangement shown wherein the rate of movement of the valve plunger is substantially multiplied with respect to movement of the piston of the master cylinder. whereby very slight' operation of the brake pedalprovides a wide-open communication between one end o f the motor and the source o f pressure differential to provide an instantaneous response of the motor to movement of the brake pedal. The same rapid relative movement of the parts isprovided when movement of the brake pedal is arrested, the piston unit 26 and the valve plunger moving relatively in opposite directions to provide an instantaneous cut oi under such conditions. It will be obvious that the relation between the area of the left hand end of the plunger 4l (Figure 1) to the internal crosssistanceto the movement o`f the brake pedal may gish response ofthe motor to initial movement be designed as desired in accordance with the relative cross-sectional areas of the 4bore 43 and pressure chamber 23.

While the motor is designed to provide vacuum suspension in; the on position of the parts, it will be apparent that any balanced pressures may normally be present in opposite ends of the motor I5. The feature of providing relatively rapid vmovement of the valve makes the motor extremely sensitive in its operation regardless of what type of balanced pressure is employed. but vacuum suspension asillustratedis preferred for the reason that it has been found to render the motor even'more highly sensitive in operation. It

also will be noted that the high rate of movement of the valve plunger relative to movement of the piston I2 is accomplished without the use of any lever means whatever and that the movement of the valve plunger is restored to one ratio automatically when the motor becomes energized l and the piston unit starts to move.

It is to be understoodthat the forms of the mvention herewith shown and described are to 'be taken as preferred examples of the same and that various changes in the shape, size and arrangeof the subjoined claims.

L I claim:

l. A brake operating mechanism -for a hydraulic vehicle brakeA system' having hydraulic brakecylinders for the vehicle wheels and a master cylinder having a pedal-controlled piston therein, comprising a control chamber communispouse since no more rapid operation of the 65 valve* mechanism is Iprovided and the amount a power-movable'potion projecting into saidv control chambergand control means for said power means comprising an [element subject to, Vmovement by yiluid displaced into said control ,chamber from the master cylinder, said-,control means having a portion exposed toA pressure in said pressure chamber to-oppose movement of movement of said second named piston and the other of which is operable by uidI displaced into said control chamber from said master cylinder,

i said second named element having a portion excomprising a control chamber communicating g with the master cylinder, a pressure chamber communicating with the brake cylinders, power means for displacing uid from said pressure chamber into the brake cylinders .andhaving a vpower-movable portion projecting into said control chamber, andy control means for said power means comprising a plunger having one fend thereof open to the pressure of fluid in said control chamber to be moved' by fluid displaced thereinto from the master cylinder, theother end of said plunger being exposed to pressure in -said pressure chamber to oppose movement of said plunger by fluid in said control chamber.

3. A brake operating mechanism for a hydraulic vehicle brake system having hydraulic brakecylinders for the vehicle wheels and a master cylinder having a pedal-controlled piston therein, comprising a control chamber communicating with the master cylinder, a pressure chamber communicating with the brake cylinders, power means for displacing fluid from said pressure chamber into the brake cylindersand having a power-movable portion projecting into said control chamber, and a vfollow-up control mecha'nism for said power means comprising a pair of elements one of which is movable with the power means and the other of which is subject toY movement by fluid displaced into said control chamber from the master cylinder, said second named element having a portion exposed to pressure in said pressure chamber to oppose movement of such element by fluid in said control chamber.

4. A brake operating mechanism for a hydraulic vehicle lbrake system having hydraulic brake cylinders for the vehicle wheels and a master cylinderhaving a pedal-controlled piston therein, comprising a control chamber communieating with the master cylinder, a pressure chamber communicating 'with the brake cylinders, a power device, a piston voperated by said power device and reciprocable in said pressure chamber to displace fluid therefrom into the.

brake cy1inders, said power device having a power-movable portion projecting into said control chamber, and control means for said power device comprising a control element subject to Voperation by fluid displaced into said control chamber from said master cylinder, said control means having a portibn exposed to pressure in said pressure chamber to oppose movement of said 'conn-ol element by fluid in said control chamber.

5. A brake operating mechanism for a hy- 4 draulick vehicle brake s'ystem having hydraulic brake cylinders for vthe vehicle wheels and a master cylinder `having a pedal-controlled piston therein, comprising a control chamber communijfcating with the master cylinder, a pressure l Achamber communicating with the brake cylinders,. a power device. a piston. operable by said said powerdevice comprising a pair of elements Yone of which is operable in yaccordance with u posed to pressure in said pressure chamber to oppose movement of such element by nuid in said control chamber. 6. A brake operating mechanism for a hydraulic vehicle brake ,system having hydraulic brake cylinders for the vehicle wheels and a master cylinder having a pedal-controlled piston therein, comprising a control chamber communicatlng with the master cylinder, a pressure chamber communicating with the brake cylinders, a differential pressure operated power device having a pressure movable member comprising a piston reciprocable in said pressure chamber to displace fluid therefrom to said cylinders, said power device having a power-movable portion projecting into said'control chamber, and a valve mechanism controlling energization of said power device and comprising a pair of elements one of whichforms a part of said pressure movable member and the other of which is a control element movable relative to said first named element to connect one end of said power device to a source of pressure differential, the second named element having a portion subject to operation by uid displaced into said control chamber from said mastercylinder and a portion exposed to pressure in said pressure chamber to oppose movement of said control element by Afluid in said control chamber.

7. A brake operating mechanism ,for a hydraulic vehicle brake system having hydraulic brake cylinders 'for the vehicle wheels and a piston reciprocable in said pressure chamber to f displace fluid therefrom to said cylinders, and avalve mechanism controlling energization of said power deviceand comprising a pair of elements one of which forms a part of said pressure movable member` and the other of which is a control element movable relative to said rst named element to connect one end of' said powerl device to a source of pressure differential; the second named element having a portion subject to operation by fluid displaced into said control chamber from said master cylinder, and a plunger movable in accordance with movement of said pressure movable member and surrounding said second named element and projecting into said control chamber.

8. A brake. operating mechanism for YYa hydraulic vehicle brake system having hydraulic brake cylinders for the vehicle wheels and a master-cylinder having a pedal-controlled piston therein, comprising a control chamber communi- Aeating with the master cylinder, a pressure chamberl communicating with the brake cylinders, a differential pressure operated powerd device having a pressure movable member vcomprising .a piston reciprocable in said pressure chamber to displace fluid therefrom to said cylinders, and a valve mechanism controlling energization of said power device and comprising a` pair of elements one of winch forms a part of said pressure movable member and the other of which is a control element movable relative to said nrst named element to connect one end of said power device toV a4 source of pressure differential, the second 4named element having. a portion subject to operation by duid displaced into said control chamber from said master cylinder, and a plunger movable in accordance with movement of said presvsure movable member and surrounding said second named element and projecting into said control chamber, the cross-sectional areas of said master cylinder land said pressure chamber, d the supi of the areas of said plunger and/gid second named element being approximately equal to each'other. l

9. A brake operating mechanism for a hyydraulic vehicle brake system having hydraulic v brake cylinders for the vehicle wheels.and a displacement of fluid from said master cylinder into said control chamber, and means operable when said power device is deenergized for eecting a flow of duid from said control chamber into said pressure chamber to replace duid leaking fromthe latter chamber. 4 Y

10. A brake operating mechanism for a hya power device, comprising` a-sieeve having its ends projecting axially into the respective chambers', the portion oi the sleeve in said pressure chamber constituting a'piston :for displacing iluid therefrom and the portion of the sleeve in said control chamber comprising a plunger, and means cooperating with said sleeve for energizing said power device and comprising a control element slidable in the second named end of said sleeve 'to befoperated by uid displaced from said master cylinder into`said control chamber.

12. Apparatus constructed in accordance with claim 11 wherein said control element has a passage through which iiuid may ow from said control chamber to said pressure chamber to' replace uid leaking from the latter, and means cooperating with said passage to close it upon movement of said control element by iluid displaced into said control chamber from said master cylinder.

13. Apparatus'constructed in accordance with claim l1 wherein the other end of said control ,v

element is subject to pressures`in said pressure chamber ancis of an area substantially smaller an extent less (than andproportional to draulic 'vehicle brake system having hydraulic brake cylinders for th vehicles wheels and' a master cylinder having a pedal-controlled piston therein, comprising a control chamber and a pressure chamber in axial alinernent and conmunicating respectively with`said master cylinder and said brake cylinders, a power device having a piston movable in one directionin said pressine chamber upon-energization of said power device to displace fluid into said brake cylinders, said power device'y having a power-movable portion projecting into said ycontrol chamber, a`control f element movable in. the same direction to-energize said power device and having a portion subject to operation by fluid displaced into said pressure chamber from said master cylinder, spring than the cross-sectional area of`said pressure chamber whereby movement of said control element upon operation of the pedal is resisted to pressures in said pressure chamber. 2

14. A brake operating mechanism for a hydraulic vehicle `brake system having hydraulicbrake cylinders for` the vehicle wheels and av pedal-controlled kpiston therein, comprising a control chamber and a pressure chamber in axial alinement` and communicating respectively with the master cylinder and with the brake cylinders, a differentialiiu'id` pressure operated power device having a pressure movable unit therein com prising a sleeve one end of which constitutes a piston movable in one direction in said pressure chamber to displace fluid-therefrom and the other end of which constitutes a plunger projecting `into said control chamber, and a follow-up Jcontrolvalve mechanism for said power device comprising a control valve element, said sleeve beir'ig ported to cooperate with said element to connect said power device to a source oi pressure diil'erential te eiIect movement of said sleeve in 'y said directiorf upon movement oi said valve elemeans urging said power-movable portion in the other direction, spring means moving said control element in the other direction, said control element and said piston having communicating passages for the ilow of fluid from said control cham- Berto said pressure chamber whnen said powermovable portion and said control element are moved to their limit in said other direction, and means for stopping communication through said passages uponmovement of said control element in the iirst named direction) V A 11. Abrake operating mechanism for a hydraulic vehicle brake system Vhaving hydraulic brake cylinders for the vehicle wheels and a pedal-controlled, piston therein, comprising --a control chamber and a pressure chamber in axial alinement and communicating `respectiyely with the .cylinder and with the brake cylinders,

"lo f 'mentjin thesame direction, one end oi said valve element being movable by iiuid entering said control. chamber from said 'master cylinder and' being of substantially smaller area than the crosssectional area o! said master cylinder to be moved inthe masteracylinder.'

15. kApparatus .constructed in vaccordance with claim-14, wherein the cross-sectional areas of said 'c rmaster cylinder., said pressure chamber andv said control chamber are pproidmately equal.

16. Apparatus constructed in accordance with in constant communication wit a source ofpar- 'tial vacuum and wherein said pressure movable .unit and said valve element are normally arranged in inoperative positions in which tliev ends o! said power device each other.

' o. moans.`

65 to an extent greater than movemeht of the piston claim 14'wherein one end o! s id power device isV are in communicationwith 

